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Can windshield washer fluid be used to deice small airplanes?
This question is related to small single/twin engine general aviation airplanes with aluminium construction. I understand that it is generally not recommended to use windshield washer liquid to deice an airplane.Based on your personal experience can someone validate this eitherways? I am looking for answers like:

Used it once and my wing fell off

or

Been doing this for 15 years with no side effects whatsoever.

As far as I know there is nothing in the POH for the planes that I'm currently flying ( C152 and Piper Dakota ). Also there is a significant price difference in the price of common windshield washer fluid and stuff like TKS. Also the question is limited to deicing the metal parts like the wings and the stabilator, not the plexiglass.

Warm water is far cheaper. I've used that very successfully to deice 1/4 inch of frozen rain. Caveats include no holdover time and should not be used prior to operation in freezing conditions.

Although it is not clear from the question, I'm interpreting this to question to be about removing minor ice and snow accumulation during a pre-flight from a plane that has been sitting on the ground, and not about FIKI.

The short answer is, you should not use windshield wiper fluid.
TKS fluid and Windshield wiper fluid are very different things first and most importantly windshield wiper fluid has no FAA approval for this kind of operation (hence the price difference). You can find a full list of de-ice fluid for ground deicing of small aircraft in table 1 of AC 135-17. AC 135-17 also provides the FAA's suggestions on small craft ground de-icing in general.
TKS fluid is not for deicing aircraft on the ground it is for in-flight fluid based FIKI systems and is pumped out of various ports and flows over the wings/surfaces. It prevents the build up of ice in flight. For ground deicing, you use FPD/ADF fluid which is a thick viscus fluid that is often sprayed on the aircraft. Ground based deicing is intended to last from the aircraft from the gate (or other static position) until airborne and thus the FIKI system can be used. it also may prevent the build up of things like snow and ice while taxing.
The reason your POH says little if anything about de-icing is because neither the Dakota or the Cessna you mention are certified for flight into known icing, thus if icing conditions prevail on the ground they more than likely prevail in the air and you are not going anywhere anyway. The typical use case of de-icing a small aircraft is getting it out for the day after outdoor storage over night during snow, freezing rain, or enough frost build up to be an issue. If the temp is warming and icing no longer prevails the aircraft may still be contaminated. In this case you would use FDS liquid to clear the surface (and possibly a brush for any heavy snow build up). Many airports will have this on hand at the FBO.
You should avoid warm water as it can freeze again if the temperature is low enough.
This question is worth reading over as well.

This is a great answer, however I suspect that the OP was asking about cleaning the surfaces before attempting the flight when there is no risk of further icing (I hope). As I said below, if you have to worry about things like 'holdover time' or cleaning an inch of ice from the wings of a C152, you are better off staying put. Judicious use of warm water (and carefully wiping it) is ok to speed up the cleaning, and the ww fluid would not hurt in this case, either.

@alexsh one can only hope but either way the advice the FAA puts forward in AC 135-17 is fairly clear and should be followed if practical. Even if icing conditions dont prevail wet wings can still build up ice.

To clarify, I only meant to deice the plane on the ground when airborne icing is not a factor.

A short answer it is relatively safe, since aluminum and steel are quite immune to interactions with various organics in the windshield washer fluid. Make sure you use the 'winter grade' fluids (they have enough iso alcohol to prevent them from freezing). I do think hot water is more effective and cheaper though so probably it is hard to find people who used the ww fluid long enough to provide reliable experimental data.
On the other hand it makes me cringe when 'deicing' (or 'holdover time') is applied to aircraft like C152 or P28A. Cleaning off ice using the ww fluid (or hot water as has been suggested) is fine if entering known icing conditions is not attempted afterwards. If your airplane has deicing boots, however, I would definitely spring for approved fluids for cleaning and treating the boots: they are quite fragile (chemically speaking) and very expensive to replace.


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Do US state governors have jurisdiction over their airspace?
Do local governments have any control over their local airspace in the US.  Could a governor singlehandedly close or restrict the airspace above his state?  I know the FAA controls national airspace but could a local government enact local measures?  And to what extent could they?

State governors do not have any control over their airspace but may have control over landing sites (read airports). From the FAA's brief on drone regulations:

Congress has provided the FAA with exclusive authority to regulate
  aviation safety, the efficiency of the navigable airspace, and air
  traffic control, among other things. State and local governments are
  not permitted to regulate any type of aircraft operations, such as
  flight paths or altitudes, or the navigable airspace.
However, these powers are not the same as regulation of aircraft
  landing sites, which involves local control of land and zoning. Laws
  traditionally related to state and local police power – including land
  use, zoning, privacy, and law enforcement operations – generally are
  not subject to federal regulation.

Yes and no.
Any governance not specifically held by the federal government is held by the state or local governments. The federal government has regulations in place that pertain directly to the National Airspace. State and local governments still retain the rights to govern any part of the airspace not covered in federal regulations. For instance, some state and local governments still allow personal ownership of airspace. Chicago, still has deeded air rights to individuals and corporations.
The administration of Air Traffic Control is a huge, complex, and expensive operation. No single local government can handle the expense. Nor can they handle the complex coordination between each other’s airspace. That, as well as the national security aspect involved, needs to be handled by a centralized government.
Airports are owned by city, state, and local governments. Some are even owned by individuals and corporations. The owners of these airfields can do with them as they please within limits. Meigs Field and Kenneth Copeland Airport are examples of this. That being said, the federal government subsidizes public airports. Since they control the purse strings, they hold a lot of sway over how the airports are run. The local governments can effectively shut down their airspaces by shutting down their airports. But, they may face major consequences from the federal government. This will not stop overflights of the area. An example of this control is the security measures put in place at airports around the country after 9/11. There were city owned GA airports that erected fences around their airfield immediately after at the behest of the federal government.
Think of it like the highway system in the US. It is too big to be left to the devices of local governments.

You suggest far more authority than governors have. With tiny, limited exceptions, they don't control airspace. Period. The feds do. Period. A governor might close an airport to takeoffs & landings (and could arguably be challenged in court for that, depending on circumstances), but it would be a huge overreach to close his state's airspace.

@RalphJ - Actually, I never commented about governors. In the specific case I mentioned, it was a mayor who shut down the airport over the desires of the federal government (the FAA). As far as shutting down the entire actual airspace, again, that is federal jurisdiction per the FAA. Just like shutting down the entire federal highway system is federal jurisdiction. As I have stated. Ownership of land rights and air rights are still given over to state and local jurisdiction. The question asked specifically about the extent of control. That extent does not have to be total control.

@DeanF. the OP limited the question to US airspace, and so individual state's power over airports, while interesting in its own right, is not relevant to the NAS. That being said, can you flesh out example of Chicago ceding NAS rights? That's really interesting to hear and I'd like to understand how it interacts with Minimum safe altitudes (14 CFR § 91.119). Are there non-gov't (e.g. city, state, federal, military) forbidden areas?

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How do linear actuators for flight controls work in fighter jets?
I've built some rc planes and know that in order to control an aileron in a rc plane, that you need a servo, a control horn(sticking out of the aileron), and a pushrod. However, I was wondering how fighter jets control their ailerons. I was researching and I found that it control is via linear actuators. I was wondering how exactly it worked and tried to look for a video or an animation. However, I couldn't find anything that explains exactly how a linear actuator moves an aileron. Can you please help me understand this with a video or something like this. Thanks so much.
This is a picture of an f22 raptor someone sent me when I asked this question on Flite Test...they didnt respond after this this. You can see orange actuators in the picture but it doesn't really help me besides that.                     https://conceptbunny.com/lockheed-martin-f-22-raptor/

Hey @Luke, can you give us an indication of your current level of understanding in regards to hydraulics. This might help structure answers better. You will need to understand general principles of hydraulics first in order to understand linear actuators. Also note there are a bunch of different designs of linear actuators.

I really dont unsterand hydraulics fully. But I undertsand the basics of how a linear actuator works. Could you give me a image or video of some of ailerons desigsn that incorporate linear actuator.

The working principle is surprisingly similar between the RC as you've described and most actuator powered aircraft. The linear actuator extends/retracts a pushrod, which is connected to a horn attached to the pivot point on the control surface.
Below is the zoomed-in picture from the OP. I've taken the liberty of highlighting the two rudder actuators and the left stabilator actuator. The one attached to the stabilator is the most revealing: the pushrod essentially connects to a horn, which translates the linear motion to a rotational one.

Ref: https://conceptbunny.com/lockheed-martin-f-22-raptor/
Due to aerodynamic and stealth reasons, this mechanism is hidden under a smooth fairing for the F-22. But for other airplanes, you can see small blisters under their control surfaces that fair the actuator. Below is a picture of the Boeing 787 aileron. The blisters have been highlighted.

Ref: https://commons.wikimedia.org/wiki/File:Low-speed_aileron_of_Boeing_787.jpg
The linear actuator itself is almost always energized via hydraulic fluid, whether it comes from a central hydraulic system or an self-contained hydraulic systems (EHA). The following diagram illustrates the working principle:

Ref: https://www.machinedesign.com/mechanical-motion-systems/linear-motion/article/21832047/whats-the-difference-between-pneumatic-hydraulic-and-electrical-actuators

Ok thank you so much. That really helped me. But are there any videos that show this system work without everything covering it so I can visually see how it works?

The last picture of the linear actuators are of the type normally used in landing gear, not flight controls. These are double acting unbalanced. The side with the rod isn't able to exert the same force as the other side without rod due to the reduced surface area of the piston (F=P*A) >>> reduced area means reduced force, therefore unbalanced

@Craig Your comments are accurate. The pictures are just for illustrative purposes. I also didn't mention all the closed loop controls required to achieve the continuous positioning.

@JZYL I dont understand how the mechanisms works though. For example I dont understand how the linear acutoar and control horn translates to the movement of control surfaces. Bassicly im looking for a animation i guess of control surfaces moving but what is happening in the indside of the wing

@LukeJustin How to do think hydraulic diggers rotate their arms then? The transformation of linear to rotational movement is exactly the same. https://www.youtube.com/watch?v=X52fB45OQjU

@JZYL I know but is their a pciture or video of an aielron rudder or stabilzer moving becuase of an actuator ?

It's really not so different from your models. Due to the strength of hydraulic actuators, those horns need not stick out into the airstream. Basically, if you move the hinge into one skin, you have most of the local thickness for hiding that horn.
Here is the interesting section from the linked picture. 125 is the control unit with the valves and 126 the actuator.

However, in order to keep forces down, a small bulge is needed on the lower wing to fair over the horn that would otherwise stick out of the surface (picture source). The near one is for the aileron and the far one for the wing flap.

Below is a diagram for the F-15: Here the hydraulic actuators are controlled via pushrods and pulleys. On more modern aircraft this will be an electric line and probably even an electro-hydraulic unit so no hydraulic lines need to be strung trough the wings (picture source).

The actuators themselves consist of a cylinder, a piston, a rod connected to the piston and sticking out of the cylinder on one end and continuing to the control horn, and a couple of valves. Hydraulic fluid is pressed into the cylinder on either end of the piston, depending on the desired piston movement. The rod then transfers the piston movement to the control surface.
The valves are controlled by cables or pushrods, as can be seen in the F-15 Lateral Controls diagram. On more recent designs, electrical control is used with a central computer calculating the best valve settings several times per second.
Why hydraulics are a good choice for such actuators can be read here.

I think @Luke is trying to ask more how these actuators work internally (principles of hydraulics), rather than how these actuators sit in the aircraft.

@Craig And your interpretation of the question is enough justification for a downvote?

I removed the downvote just now because you have added the last section that explains how an unbalanced linear actuator works. Respectfully, before your edit, it was just some pictures that showed their location in the aircraft but not anything about how they worked.

@Craig I agree, downvoting random answers is much more helpful for the questioner than – beware! – adding a better answer yourself. I'm sure he will appreciate your invaluable service.

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Does the yoke move when trimming a THS like it does when using elevator trim?
I would like a clarification from the operational point of view:
Both the THS and elevator trim tab is used to remove pilot pressure on the yoke / stick.
On the elevator trim similar to the C-172 the yoke deflection is a function of the speed: so in trimmed condition the yoke deflection depends on the IAS we what to fly.
What happens on the THS trimming? Does the yoke deflection always stays in a "center" position after trimming or the behavior is similar to the C-172 ?

Does this answer your question? What are the advantages of a Trimmable Horizontal Stabilizer?

I am talking about the yoke/stick deflection of the two systems.

@ManuH Could you show where exactly this question is answered in the linked duplicate. I cannot find it...

@Bianfable the original question was "THS vs elevator trim" (see edition history)

When I was type rated in the CRJ200 with hydraulic controls and a THS, directly coming from light aircraft, the differences in technique are significant and it was definitely something new to learn.
With a THS, column neutral is always the same spot.  This means trimming to a speed is not a case of moving the control to location X and trim until it stays at location X. You have to apply a control input to achieve a speed/attitude, and trim until you can relax the control input and let it go back to its "permanent" neutral position while the airplane maintains the target trim speed.
So what you do is, say, you want to slow down from 200 kts to 180 kts, so you pull and hold to slow down. While you're holding the input, you start to blip the trim switch with your thumb as, at the same time you let the column move a bit back toward neutral.  The objective is to make the trim input as you relax the control input so that the stab incidence change is replacing the elevator deflection and the airplane holds a constant attitude and speed.
You keep doing this; blip-release-a-bit, blip-release-a-bit, blip-release-a-bit, until the column is back at neutral and the plane is holding your target speed with no input.  With practice you start to pull and blip the trim right away and it all just flows automatically.
It's murder on the trim screw jack drive systems, because they get many many start/stop cycles a flight from pilots going blip-blip-blip on the switch whenever they are hand flying.  The autopilot also does the same thing, sending numerous trim pulses to trim out speed changes to offload the AP drive servo.
Light planes with trimmable stabs, like the Cessna 180-185 family, are very similar, because the elevator just wants to "trail" when hands free, and the neutral position doesn't change the way it does with a tab, although it varies a little compared to a jet with hydraulic controls.

so in trimmed flight condition a THS ac  the yoke is in the same neutral position disregarding speed and CG. The trimming procedure is then different from the elevator trim tab of the cessna c_172. THS requires to trim to get neutral position of the yoke while the elevator trim tab requires to trim in order to maintain the actual yoke position.

Exactly.On a jet with cables and hydraulic control surfaces, the control cable loop's neutral, set by a pitch feel system of some kind (on the RJs it's a box with bungee springs inside, that are the actual force you working against when you move the column) never changes.And elevator neutral is always aligned with the stab chord line. Linkage geometry at fin/stab keeps this neutral relationship as the stab's incidence is varied and is transparent to the pilot. So the only time the elevator is not aligned with the stab chord line is when you or the autopilot makes a temporary maneuvering input

I am only talking about yoke/stick displacement. Jjust to summerize: is my previous statement correct ?

Yes. If you make a trim input, the yoke doesn't move.


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Is there other option than a Chinook to transport 2 cars simultaneously?
If a civilian wants to fly between homes several hundred miles apart AND carry 2 cars with him what are the options other than a chinook?

First, does it have to be a helicopter? Second, is there some reason you can't just keep spare cars at the hangar on the other end?

Are we talking a couple Humvees, or Smart FourTwos? If you can afford the helicopter, having spare cars shouldn't be an issue...

Also, let me be the first to say: If you are someone who’s genuinely capable of considering a private Chinook to transport vehicles back and forth between your 2 homes, I’d like to officially offer my services as a pilot. I’m a helicopter pilot with multiple airplane ratings as well. I’ll even long line your cars directly onto your driveway,

Another alternative: pay two drivers to take the cars while you fly. Make sure to have one car leave early so you have something to drive at the other side

Nice problem to have :D

Sounds like an XY Problem to me. What are you really trying to solve, or is this just speculative?

Yeah, depending on the cars, it’s gotta be WAY cheaper to buy a few spare vehicles and go with a smaller helicopter.  Of course that might not impress the neighbors as much, in case that’s your goal...  :)

@FreeMan, thanks for the link to the XY problem!  Brilliant, and applicable so often and in so many ways.  Definitely in this case.  At work my first step was always to come up with a clear problem statement.  I.e. “the goal is ___, the challenge is ___, it’s a problem because ___, the options are ___.”  Just taking the time to do this can sometimes produce the clarity needed for an obvious solution will pop out.

I think you should precise what kind of cars you want to transport. Transporting 2 vans is not the same as transporting 2 smarts

@MichaelHall: In programming, there is the practice of rubber ducking, which is literally just explaining the problem to a rubber duck sitting on your monitor. (You can tell this practice is older than flatscreens :-D ) There's also a famous story of a professor who instituted a rule that you could come to him at any time with a problem, provided you explained the problem to his assistant first, and the assistant couldn't solve it. The number of students disturbing him dropped dramatically, since it turns out most problems were solved by the assistant.

The twist: the assistant was a teddy bear. The "Stack Exchange Effect", where you compose a question only to delete it before posting because you found the answer is also related.

Manu H may have been alluding to this, but to any prospective Chinook buyers out there:  CHECK THAT YOUR CARS WILL FIT.  It's really more of a medium-lift helicopter than heavy-lift.

@Kevin Duffield, well... did you find a useful answer here?

You could use an Mi-26 to transport your two cars, as seen here:

With a payload of up to 20 tons, it should be able to lift many useful combinations of two vehicles.

Yep.  Accept this answer and go buy one now.  Problem solved.  See how helpful we are here?

Sorry. I’m not laughing at this. It’s something else...

NIce cars there.

Top Gear demonstrated that 3 cars fit comfortably in an Ilyushin Il-76. And that it can be hired.

You can back right into the cargo hold up the loading ramp, and drive right back out again when you get to your destination.

Designed to operate from unimproved (unpaved) strips and with a 1,500 foot landing roll capability (using thrust reversers), it's the clear and proven choice for your civilian car transportation needs.

No go. The OP wants to transport 2 cars, not 3.

Can't he buy a third car and leave it in the Ilyushin?

@RainerP. But then they have to decide which car to buy third. Imagine how long that can take. First they'll have to create an account on the Mv SE...

But the OP may not have a 1500 ft strip at one of his houses.  For instance, I think there are houses built on private inholdings within national parks & monuments.

@jamesqf Admittedly this is indeed an impractical answer to an impractical question. But that was precisely Top Gear's forté and I couldn't resist :)

Also, although you may get the Il-76 down in 1,500', you certainly won't get it back up again, at least without JATO (which I don't believe the Il-76 was designed for).

@Therac I thought it was a fantastic answer that focused on the exacting requirements of the original specification. Why spend more jet fuel than you need to? lol

In all seriousness though, I believe OP intended to request a chopper rather than a fixed wing.


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How many LRUs are there in modern aircraft like a Boeing 747 or an Airbus A380?
I work in the Avionics industry. I always wonder, how many Line-Replaceable Units (LRUs) are present in modern aircraft like A380 and Boeing 747.
I understand that number of LRUs varies from customer to customer. I just want to know in general how many LRUs present in an Aircraft.

"modern" is rather loosely defined here - the 747's first flight was in Feb 1969!

Yes :-) But still it had many iterations (small updates)

It's difficult to precisely answer your question, because they are not public information and depend on the aircraft sub-model, customer configuration, etc.
I built this approximate plot using the data from [1] that shows the trend in Airbus models:

It should be quite surprisingly to you that the A380 has the same number of computing units of the A340. This is because of the transition from the LRUs design to the IMA design (see this question for the difference), that allows to considerably reduce the number of computing units required, called Line Replacement Modules (LRMs). Airbus claims they were able to cut the 50% of the required computers in A350 thanks to IMA approach [2]. A similar claim has been made by Boeing for the 787.
The data does not show the recent aircraft models, but I expect they are still around 100 or slightly above on newer aircraft like A350XWB (which shares most of the A380 avionics). This is because increasing the number of avionics computers is very problematic as it has terrible cascade effects:

This conceptual diagram may look exaggerated, but consider that Boeing claims the reduction of 2000 lbs (~900kg) switching from the LRU approach to the IMA approach [3]. Saving 900 kgs means adding 10 people to the cabin, and it's easy to imagine the money saved by the airlines in the lifetime of the aircraft.
Anyways, check this video which shows the avionics bay of A350XWB: pretty impressive.

Hey @ocirocir, thank you for your answer!! sorry, I read your answer after long time you answered! Thanks again! Great explaination!


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Why is bleed air taken from some stage of the compressor used for de-icing? Why not e.g. exhaust gas?
In the answers to this question, it is said that

The de-icing system on most turbine aircraft (including MD-82 involved in that accident) uses bleed air from the engines, that is it extracts some air from behind the (low pressure stage of the) compressor. This air is therefore not ejected from the nozzle and not producing thrust, so the thrust is reduced.

My question is:
Why is bleed air taken from some stage of the compressor used? Why not e.g. exhaust gas?
For de-icing, the temperature of the used medium must be above 0°C (melting ice), while the environmental temperature usually is far below.
So the engine has to invest energy to generate bleed air with reasonable temperature, the air cools down to still >0°C during de-icing, and is then vented out to the environment.
There, it expands and cools down far below the environmental temperature.
This expansion means that energy is wasted, and also, when the bleed air is cooled down / expanded before inserting it into the de-icing system (I don't know if this is done), energy would be lost.
In addition, air/pressure is lost in the compressor stage, which makes the combustion less effective. (Again, I don't know how much air is taken, and how big the effect is)
On the other side, the exhaust gas of the engine is very hot due the combustion and could be used without the need of extra compression. So, using some exhaust gas, one would not waste so much energy. If it's too dirty, heat exchangers could be used to heat fresh air.
I would think of this reasons

Bleed air is anyway used for many purposes in an aircraft, so this is more economic than a completely separated system
De-icing is not used for long time during flight, so again no need for a dedicated system

EDIT:
I'd like to expand the question to explain what makes me curious. In the comment, the correctness of this sentence is challenged:

There, it expands and cools down far below the environmental temperature.

This is a simple thermodynamic process. The air is compressed adiabatically, i.e. without adding heat to it. The heat comes from the thermal energy of the air, now also compressed to a lower volume.
De-icing cools down the air, and when releasing the air to the environment, it expands to the orignal pressure. As thermal energy has been removed during de-icing, the temperature drops below environmental temperature.
Here is the math behind:
The relation of pressure and temperature in this case is:
$$ p_1^{1-\gamma}\cdot T_1^\gamma=p_2^{1-\gamma}\cdot T_2^\gamma\qquad \gamma
\approx 1.4$$
Let's assume a pilot switches on de-icing during flight at 11km altitude. There, environmental pressure is 0.25bar (atmospheres) and temperature is -50°C (223K). It was also said here in the answers that it's possible that the bleed air has about 200°C (473K).
The formula now gives a bleed air pressure of 3.47 bar, so a pressure ratio of about 14. The air is now cooled down while the pressure is maintained by the engine. I assume de-icing will be effective for bleed air temperatures above 0°C. So if the air is released at this temperature, the temperature will fall down to -144°C (128K). Another number: If releasing at 100°C, the temperature will drop to -97°C (175K).
(Of course, the air will mix with the environmental air immediately)
In principle, one can play with the numbers, increase/decrease altitude / temperatures and discuss how adiabatically this (de)compression processes are.
Anyway, this is a big air conditioner, using the thermal energy for de-icing and wasting the cooled air. If one only needs hot air, something coming from the exhaust system would always be more efficient.
This is not really efficient. May be the bleed air behind the de-icing system can still be used for other purposes, as it still has the pressure?

You say that the bleed air "expands and cools down far below the environmental temperature". That's just nonsensical. It might cool down to environmental temperature (it does eventually) but hardly below it. I think that passage should be edited either to be corrected, or to be clarified.

Yes, it does! I edited my question concerning this (and now notice the question is more than twice as long as before...)

@sweber I don't think the second part of the question fits here.  But keep in mind that the hot pressurized air is moved along the wings at high pressure, loses its heat, and only becomes low pressure (and therefore very cold) at the point of release into the atmosphere.  At that point we don't care how cold it gets - and yes, it does get colder than the intake air, and it does essentially form an air conditioner.  But the engine exhaust is ejected with the turbine airflow.  Anything else in that specific path will be less efficient overall than bleed air.

Particularly when you take into account that wing de-icing doesn't have to be on all the time.  But placing something in the exhaust/turbine path will always reduce engine efficiency whether in use or not.  So even if it's less efficient when in use, over the life time of the airplane and during most flights it is more efficient than exhaust gas.

Using air from the exhaust section either for anti-ice directly, or using a heat exchanger, would create many problems.

The air must first be used to burn fuel before reaching a turbine bleed location. Air taken from the compressor section hasn't required any fuel to be burned (other than to compress that air of course).
The air will be much, much hotter than air from the compressor. Turbines, especially in the high pressure section, are made of specialized alloys and can be additionally actively cooled to prevent them from melting. This means more specialized, and therefore more expensive and/or heavy material must be used for the whole anti-ice system.
Components must also be designed for the case of this bleed air leaking. Hotter turbine air would be a huge problem for this.
The air will have the combustion byproducts in it. This can coat the insides of the anti-ice system, reducing its effectiveness, and possibly requiring it to be disassembled and cleaned periodically.
If there is some type of engine fire, the fire typically goes downstream, which would send it into this anti-ice system as well.
In the case of using a heat exchanger, this would be yet another component to fit into spaces that are already very full, and yet more weight on the airplane.

The air from the compressor is already plenty hot. Take a look at the diagram in this answer. Notice that all the compressor bleed air goes through the precooler before going to cowl or wing anti-ice. This means that the compressor air is already hotter than is required. So taking air from the turbine provides no benefit for creating the problems listed above.
Also, taking air from the compressor does reduce engine efficiency, but you are going to have to get that energy from somewhere.

To address your points about the thermodynamics:
Assuming your numbers are correct, what is wrong with that scenario? Releasing air at -97°C that was initially at -50°C means that you extracted 47°C of energy from it to use for anti-ice, using the systems already available on the aircraft (bleed air, precooler). Kind of like a heat pump, but just using air? Wouldn't it be less efficient to burn fuel to heat this air, which would then leave the aircraft at a higher temperature, and therefore throwing away more energy?

In principle, one can play with the numbers, increase/decrease altitude/temperatures and discuss how adiabatically this (de)compression processes are.

(Emphasis added) I'm not convinced that your assumption that these processes are adiabatic is a good basis for your model, since that is an idealization (though your initial bleed numbers do seem to match here and here). An important point is the way the air is used. A typical installation uses piccolo tubes. Small holes along the tubes release the air onto the leading edge. This whole leading edge cavity then vents to the environment. (This doesn't seem to match your assumption that the air is cooled at constant pressure) In order for this air to be useful any further, you would have to somehow return this air to for reuse. This adds more complication, when there is already an abundant supply of compressed bleed air available.
Another option would be to somehow maintain the pressure behind the surfaces with ice protection. This may be feasible for the engine inlet, but not for wing leading edges that include moving slats.
Even assuming you can somehow recover this air for use, that would be another system and more complication added to the aircraft. And you can't rely on this system, because anti-ice is not always in use. You have to provide a pretty large gain in efficiency to justify adding weight and complexity to the airplane.
Maybe you would like to see proof that most the work done on the air is used in the anti-ice process, and adding heat from combustion is not necessary. We may need to get someone like Peter Kämpf in here to run some numbers.

also keep in mind that exhausts will contain much more water as a result of the burned fuel than only compressed air, which might also be counter-productive depending on the environmental conditions.

Your first reason is the major one: Bleed air is abundant (jet engines generate far more than they "need" for operation), already hot (typically well over 100C), and produced at a relatively high pressure - that's why it's tapped for things like anti-icing systems, cabin air conditioning, and starting other engines.
It takes little effort in design to install another valve in the bleed air system to direct the flow to anti-icing systems.
Capturing the turbine exhaust (hot combustion gasses) would require its own special hardware (valves, ducts, etc.), and measures to cool the combustion gasses to a temperature the anti-ice system can handle (heat exchangers), which means more complexity and more weight, so if an aircraft already has a bleed-air system available it makes sense to use it for the de-ice/anti-ice system rather than add another equally-complex arrangement to capture combustion gasses.

For "bleedless" aircraft (ones that don't have the ability to pull bleed air from the engine's compressor) alternate de-icing systems are used (e.g. the 787 uses electric heating elements).
These could also be used on aircraft with bleed systems, but they have their own disadvantages in terms of maintenance, weight, and complexity. (Bleed air anti-icing systems are comparatively simple: a few valves and tubes with holes drilled in them to let the hot air out where it's needed. Maintenance and upkeep are fairly trivial.)

I'll agree with the first sentence except in takeoff and climb where a/ice activation can have a noticeable impact in performance.

@casey Yes, obviously in any phase of flight requiring all the power the engine can produce any system which taps that power (for whatever purpose) could have a noticeable impact.

Also note, that the electric system reduces engine power as well, because the energy still needs to be taken from somewhere and the generators are driven by the engines.

I agree with you that the bleed air ends up colder than ambient, but not that this "means that energy is wasted".
On the contrary. Once the portion of air we're using is back at ambient pressure, it will be colder than before the engine took it in. That means that heat energy has been removed from it. Where did that energy end up? The only place for it to go is in the wing surfaces that we wanted to heat up. (This assumes that the piping and so forth is thermally insulated so well that we can neglect unwanted heat losses there).
The net result is that the amount of heat energy deposited in the metal of the wings is larger than the mechanical energy we used to compress the air in the first place. Which sounds pretty efficient to me.
On the other hand, engineering for the de-icing air to be warmer than strictly necessary after we're done with it, that would be a waste.

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What if pilot feels too tired before his flight?
Today is a day when I feel terribly tired. I'm not ill, but I could sleep all the day, though I had enough sleep last night.
This is not a problem if you have an office job where you can probably be not as productive than on other days. But what about pilots? They are expected to have a high level of concentration and vigilance during the whole flight?
This question, What should a pilot do if they feel sleepy? concentrates more on upcoming sleepiness during the flight. The accepted answer says:

If a pilot is not rested enough to safely operate the aircraft, they should not fly. [...]

Well, "should not" sounds more like  advice than a rule.
You may say that there are always two pilots on (not so long) commercial flights, but then you can also start with one faulty engine, because the second engine still could bring you to your destination. For me, this breaks the safety concept.
So, can a pilot go to a doctor and tell, "I'm tired today so I can't work"?

So if you are well rested and not ill, but still feeling tired, there has to be something else wrong. From your description, it appears to be fatigue. The common signs for fatigue are:

Falling asleep
Yawning
Poor visual acuity
Feeling "sluggish" or "drowsy"
Decreased reaction time
Decreased concentration

Although, the most commonly known reason for fatigue is lack of sleep, but any or all of the following can cause fatigue:

Lack of quality sleep
Sleep disturbances
Interruption of circadian rhythm
Mental or emotional stress
Physical exertion, such as heavy exercise
Poor health, including dehydration or poor diet

Pilots can assess their own fitness to fly by the IMSAFE mnemonic. FAA has a small handout about fatigue.
Now what pilots (and generalizing, people) can do and actually do are two very different aspects. A survey about European pilots mention:

... many are afraid their fatigue reports could have negative
  consequences for their professional future (i.e. reprisals by
  management) ...

FAA has a new rule which states:

The FAA expects pilots and airlines to take joint responsibility when
  considering if a pilot is fit for duty, including fatigue resulting
  from pre-duty activities such as commuting.  At the beginning of each
  flight segment, a pilot is required to affirmatively state his or her
  fitness for duty.  If a pilot reports he or she is fatigued and unfit
  for duty, the airline must remove that pilot from duty immediately.

The answer to your question is: Yes, they can!

Although it really doesn't happen a lot - compare the number of days you feel exhausted in work, with the proportion of flights you've ever known to be cancelled (for any reason)

@JonStory When did I say that it really happens a lot? Regarding the comparison between my job and a commercial pilot, they cannot be compared as they are entirely different. Commercial pilots do not work 8-9 hours a day, 5 days a week, every single week. What is your point?

I was more adding a 'food for thought' comment adding to what you said :) I don't we anything wrong with your answer

@JonStory Ah, thanks for the clarification. I didn't get it at first.

@Farhan: Commercial pilots do work as much as you and at irregular schedule to make things worse. I asked about that some time ago and while they have 100 flight hours monthly limit, the additional duty time on ground (pre-flight, post-flight, time while loading etc.) can easily make once as much (especially when flying short routes) and they end up with ~180 hours like normal office worker.

never underestimate mental stress as a big reason for fatigue.

On top of the number of hours that commercial pilots work, you should also consider the amount of time that they spend away from home when comparing the job to a typical office job...

@JonStory the flight isn't likely to be cancelled because a pilot is tired, that is why airlines have standby crews.

"So, does a pilot go to the doctor and say "I'm tired today, I can't work"?"
Simply put, "Yes.  Say you cannot work.".
If a surgeon cannot operate with full facilities, he doesn't operate.
The patient can have surgery tomorrow (in most cases).
If a pilot cannot be assured that he can perform, regardless of weather, mechanical issues, ATC delays, whatever, the passengers can be inconvenienced.It is better than the alternative, which is ending up dead.

If you feel so tired and fatigued that you cannot safely operate an aircraft or perform your duties as a member of a multi-person flight crew, it is your call to do so, but yes, you can call in to a supervisor and tell them you are simply unable to fly.  I don't know what the law is exactly but it is probably illegal for an employer to discipline you or to terminate your employment for a single instance of this.
Multiple and/or frequent infractions could lead you into trouble with an employer as it is your responsibility to plan ahead and be well rested and nourished for a duty shift.
This issue garnered a lot of attention with the crash of Colgan Air (Continental) 3407 in Buffalo in 2009.  CVR tapes revealed a flight crew frequently yawning, and the FO complaining about long duty schedules as well as being ill and the cost of getting a hotel in order to get well.  It turned out that many commuter outfits were working pilots through 14-16 hour duty shifts plus commuting with very little concern for their well being aside from management demands that they "move the rig".  See the program Frontline: Flying Cheap.

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Had there ever been an commercial jet aircraft accident caused solely by too many passengers?
I've been researching on a rather weird but interesting subject: had there ever been a plane crash or other accident that was caused solely by too much people crowded into an aircraft (not cargo, but humans, either passengers or crew)? Because I know that overweight cargo had caused many crashes but I've never seen or heard any crashes related to too much people being crowded into aircraft (although sometimes they are depicted in movies). Is there any such occasions? I mean, had human weight ever brought down an aircraft? Thanks for any answer!
Note: I'm looking for accidents involving either large jet aircraft (like Boeing 727, 737, 747, 767, 787..., or at the very least turboprops such as ATR-72), or accidents that involve at least 50 fatalities.

Just out of curiosity: the Concorde that crashed in Paris was also slightly overloaded (but that was not the direct nor the indirect cause of the incident)

Accidents do not have a single cause.

@Bianfable Thanks you for pointing that out. Boeing 727 and 737 are indeed narrow body aircraft, sorry for the mistake. I will edit my post to reflect this correction.

@AnonymousPhysicist Yes, I agree that accidents don't have a single cause, but there are usually at least one main contributing factor or the main cause. So I'm not looking for crashes caused by only overloading, but I'm looking for crashes that overloading was the main factor and no other main factors exist.

Any comment from downvoter? As always, please add a comment to inform me of any problems/mistakes/wrong behavior so that I can edit this post to improve and avoid these errors next time.

Any comments? I've got another downvote. Please do tell me how I can improve.

People usually fly with luggages, especially in widebody aircraft. Do luggages count as a factor ? Let's say you have military passengers with their 320Kgs equipment per person in the plane ?

@KarlStephen No, my question's intention is focused solely on the weight of people, not including any cargo or luggage. Sorry if my question isn't clear enough.

In that case, your only domain is "obscure flights" with no records whatsoever : Africa, possibly South America, Asia and Middle East (Hajj) in the 60s-80s era, decades ago when safety was less strict worldwide and people were flown in cargo planes, especially during war. You probably won't find any conclusive investigation, many tinted with politics where versions depends on who's talking. Documented airlifted people may have been conducted at slightly over MTOW, but all went pretty well. The C5 Galaxy crash during ops Babylift was caused by a structural failure, not weight.

I mean, the answer to your question is "NO, not a single one", as on AviationSE, we need/require documentation/sources. Opinion based thoughts says "we don't know for sure", but, for airliners with logged flights, there is not a single aircraft of the category you specified which crashed because of people weight. The downvotes (I didn't) are likely related to the fact any opinion-oriented answer to your question is invalid here, where, only an opinion-based answer could have either "yes" or "maybe".. As for the early ages of aviation, yes, pilot weight did bring many small attempts to fly down

@KarlStephen The answer I accepted did answer my question and is not opinion-based. Although the crash of Arrow Air Flight 1285R is blamed on a multitude of factors, one of the primary reasons is icing and overloading. And although the "overloading" does include luggage, the number and weight of passengers also played a significant role.

Downvoters, can you please tell me how to improve? I mean, this question had been downvoted many times, so I figured there must be something that I can improve. On the other hand, however, the answerers here did a great job at explaining the problem and providing interesting cases and great answers, so I think my question is not completely inscrutable or off-topic. So, if there's any space for improvement, please tell me through the comments and I will try my best. Also, please stop the downvoting if you don't have anything to say.

Maybe not solely, but Yes. A flight carrying a company of US Army 101st Airborne soldiers returning home from the Middle East crashed on takeoff from a refueling stop in Newfoundland because their average weight was much higher than the standard average passenger weight that burocratic standard FAA airline procedures used to calculate aicraft gross weight and takeoff performance.

Thanks for your answer, I'm really interested in this case. Can you please edit your answer to contain information regarding the type of aircraft, flight number, and (if possible) the NTSB's report on the accident?

There was a famous Gander crash that sounds similar to this, Arrow Air Flight 1285R, but that wasn’t the stated cause.

@300D7309EF17 Are you two talking about the same crash? Because I couldn't find any other accidents having the same details: US Marines returning home, crashing in Canada, ... So, Charles Bretana, are you talking about Arrow Air Flight 1285R?

Yes, I am referring to Gander Arrow 1285 crash. Attached below is quote from history doc:

The Canadian Aviation Safety Board's (CASB) extensive investigation of the crash of Arrow flight 1285 is not expected to be completed until early 1987. Preliminary findings indicate that the crash was likely caused by the unfortunate confluence of a number of factors, no one of which would have been sufficient to bring the plane down. These included icing on the wings, mechanical problems, and crew fatigue. Overweight conditions in the passenger compartment due to the large amount of carry-on luggage also might have been a factor.

..... Passenger and carryon luggage weight was not determined prior to take-off at Cairo, but the Arrow flight crew had estimated that the average weight per passenger, including carryon luggage, was 170 pounds. The CASB calculations indicated that the average weight per passenger with carryon luggage was at least 220 pounds.

You can read more here:   https://history.army.mil/books/dahsum/1986/appa.htm

@CharlesBretana Thanks a lot for the added info! Although I knew of this crash earlier, the details you provided really helped me understand the causes of the crash better. Again, thanks!

Yr very welcome!

If you have YouTube, also check out Air Disasters episode on this crash...

Aaliyah's crash in the Bahamas was definitely caused by too many people on the plane. This happens with small piston-powered planes flown by incompetent operators. It does not happen in commercial flights where enforcement of gross weight and CG balance restrictions is part of standard operating procedure.

Thanks for the answer, but I'm looking for commercial flights (think Boeing 737, 747, 767, 727, 787,... or at the smallest turboprops like ATR 72) , not chartered Cessna aircraft. I might be looking for some crashes in the old days of aviation, when regulations weren't as strict.

@AircraftEnthusiast007 you should edit the question and title to indicate this.

@300D7309EF17 Thanks for the suggestion, I've already edited my post to reflect what I want.

A chartered aircraft is by definition a "commercial" flight.

@randomhead Yeah, but I stated in my question that I'm looking for crashes involving aircraft with the size of at least turboprops like ATR 72. I hope that is clear enough to understand that Cessna crashes and accidents aren't what I'm looking for. The problem is not "Chartered", it's "Cessna".

Wasn't the CG balance problem caused by an unexpected one ton extra luggages ?

In 2003, Air Midwest Flight 5481 crashed. One of the causes was incorrect calculation of passenger weights. The average was 20lbs low, the plane took off at 105% of its maximum weight.


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Aircraft pitching forward when gaining speed during takeoff but also forward when stalling?
Aircraft with conventional landing gear are tilted back when at stop/low speeds on the ground, but then when they gain speed they pitch forward (so they're level). Is this because of increased speed and lift from the rear surfaces? I assume it's related to aerodynamics.
However when the aircraft is flying and stalls, doesn't it also pitch forward (nose down)?
This is confusing to me because why would it pitch backward (nose up) due to slow speeds on the ground but pitch forward (nose down) when at slow speeds in the air?
I obviously don't have any piloting experience. The reason I'm asking is I'm making an arcade-ish flying game and I'm using lift and gravity and other forces in the physics engine. I need to figure out why planes are behaving like that so I don't have to hardcode the plane on which way to pitch depending on whether it's on the ground or in the air.

For airplanes with conventional landing gear, their center of gravity is located behind the main gear. This is what allows them to sit on their tail on the ground. You are correct that as they gain speed the air flow over the tail eventually becomes enough to lift the tail and bring the plane into a more level attitude.
Once the airplane is in the air, the wing is what's supporting most of the weight, not the main landing gear. When a wing stalls, the center of pressure (where the remaining lift is being produced) moves backward. This pushes the tail up and the nose down. The stall also changes the air flow over the tail, reducing the downforce there and making it even easier for the tail to move up and the nose to move down. See the answers to this question for more detail on why airplanes tend to pitch down when they stall.

However when the aircraft is flying and stalls, doesn't it also pitch forward?

Yes correct, but for a very different reason.
Without entering in mathematical and aerodynamical details, when an airplane flies the following aerodynamic forces and moments act on it:

Lift $L$ created by the wing and acting at a distance $X_L$ from the CG;
Pitching-down moment $M$ created by the wing;
Lift $T$ created by the tail and acting at a distance $X_T$ from the CG.

Lift $L$ and moment $M$ make the airplane pitch nose-down (just think the CG like if it were an hinge) so that a negative lift $T$ is normally required from the tail in order to give a counteracting (nose-up) pitching moment:

An A350-1000 in flight. Source, modified by me
Now, when the airplane stalls this equilibrium is upset since:

$L$ decreases;
$M$ increases (normally quite a lot); and
$T$ decreases.

The net effect of these modifications is an increase of the total pitching-down moment which is no more counteracted by the tail's pitching-up one.

I need to figure out why planes are behaving like that so I don't have to hardcode the plane on which way to pitch depending on whether it's on the ground or in the air.

I fear you have to differentiate between when the airplane is on ground and in air since the landing gears do change the behaviour quite a bit.

Why would it pitch backward (nose up) due to slow speeds on the ground but pitch forward (nose down) when at slow speeds in the air?

Short answer:  Because the main landing gear gets in the way.


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How would you improve the landing gear in the WW2-era Spitfire?
I've read that the last improvement done to the landing gear was the shock absorber, but what else could be changed as an improvement?

Welcome, and your English is fine.  I'm curious why you think it needs to be improved though.  Were there problems with it?

@MichaelHall , Thank you!  It's not that I think there's a problem with it in general. But there have been many technological advances since those times, like the materials that are used; it was sharp tech back then. It's one of my favorite aircrafts but I'm not very familiar with it, I only know what I've read online. If you could recommend any articles about the Spitfire for me to read, I would be grateful!

The main problem with the Spitfire's gear was the tire track was very narrow, which made it easy to tip over while turning, especially once slowed down to where the ailerons were ineffective. This was structurally advantageous, because the wing didn't have to take landing loads, the gear being attached at the wing roots, but there was a price in handling (the Me 109 suffered the same problem for the same reasons, and was reputed to be even more exciting than the Spitfire with a very high rate of losses from takeoff and landing accidents).
The main fix to improve the gear would be to do what most other later WW2 fighters did, which is move the gear legs outboard on the wings to improve its ground handling by making the airplane resistant to tipping on a wing tip if the plane swings too hard. This is heavier structurally though, but worth the price because of the reduced ground loop accidents.

Would it be a half way substitute to make the landing wheels wider apart but maintain the mount point in the wing root?  That would give a wider track at the cost of longer legs, posititoned at an angle and needing cross bracing or more strength.

You could, but you would want to cant the wheels to keep them vertical, and this increases the vertical space required to enclose them when retracted. The Me109 splayed the gear like that, but kept the wheel axis perpendicular to the  gear leg, so the wheels roll while tilted inboard 10 of 15 degrees. The result is each wheel wants to roll in a circle toward the opposite side (like a turning bicycle). When weight is transferred to a given wheel during a swing, that wheel wants to turn toward the opposite side amplifying the swing. That's what made the 109 so hairy when rolling on the ground.


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Who is this flyer seen in Oakland, California c. 1929?
Who is the man on the left? Second from left is W.A. "Sandy" Sanders, third is Denny Wright, and fourth is Clyde Sunderland.

Oakland, around 1929.

Are we supposed to know who "Sandy" Sanders, Denny Wright, and Clyde Sunderland are? A google search (for your last question) revealed that Clyde is a photographer, but I don't know who the other ones are (nor does a search help) and how they are related to aviation history?

Thank you for your question, it is well taken: I am fishing here, and I hope I am not abusing the forum.  Wright and Sanders owned and ran "the oldest aviation school at Oakland Airport".  (photo to follow).  Clyde Sunderland is the real bait here. He was not just 'a photographer' ( https://gregyoungpublishing.com/clyde-sunderland/), he is considered to be on a par with Ansel Adams. There are few pictures of he, himself, however.  So, yeah, I was hoping for some bites.  Early aviation history is turning out to be much more localized than I expected.

I have very much found this question off topic as at Aviation SE we are here to ask questions, not to identify people

@super, there is a photo showing two pilots managing an aviation school and another one being a lead character in aerial photography. The two businesses where conducted at Oakland airport. The fourth person could be a pilot too. Identifying pilots is not that different from identifying aircraft or aviation places.


text:
Which weather condition causes the most accidents?
Among all weather conditions (fog, hail, snow, thunderstorms, etc.) which one causes the most accidents?
Note: Ideally I want to limit the question to accidents within general aviation for typical single-engine aircraft like the Cessna 172.

Wind, gusting in particular, accounts for more accidents than all other weather conditions combined.  Temp/humidity/pressure comes second, causing carb icing or high density altitude.  Precipitation (under Ceiling/visibility/precip) is a distant third, mostly about low visibility.  "Convective weather" accounts for just 39 accidents, mostly thunderstorms.
The closest match to "Cessna 172" is "Flight operation type: Personal," shown here.  Removing that filter yields similar ratios.
This is from the NTSB's 2012-2021
General Aviation Accident Dashboard, page 2 of 3.

Something doesn't make sense about the whole graph

@Gabe Can you elaborate please?

Makes perfect sense to me - do you just disagree with the data? Or the categories?

@EndAntisemiticHate The problem with the graph is that the numbers don't add up. There are 7943 "Accidents with Findings" in the leftmost column, which are split in 5 categories: you'd expect those five numbers to add up to 7943, but the first two alone are already over 12 thousand. And the same goes for every other column. I suppose it means that for every accident there is more than one cause, which totally makes sense -  but it does make the graph harder to interpret.

Since there might be several causes, the conclusions drawn in the answers while probably mostly correct, can be a bit imprecise. As an example, what if an accident happens in low light conditions with wind? perhaps low light conditions would have been enough...

Moreover, and this is by far the biggest shortcoming of this analysis, we lack information about the relative probability of all the conditions above. Wind is something that is almost always present, and it follows quite easily that it can be a predominant cause. If one of the categories was "hurricane", with one accident, nobody of course can say that hurricanes are safer than wind - which is not something that OP tries to claim by the way. One could also say (silly example) that in 100% of the accidents the pilot was present and therefore flying without one is better :)

All of that said, I still thing that this gives a pretty good indication of when one should be particularly wary of the situation, and the data is interesting, just to be taken with a grain of salt.

@Gabe in most accidents, there is no single cause, but several causes, which all put together, resulted in the accident. e.g. icing + did not use de-icing = accident. This explains the Category. In Subcategory, it seems some contain others, in particular "Physical environment" also contains "Conditions/weather/phenomena".

@VladimirCravero: Right. The first thing I said to myself on seeing this data was "base-rate fallacy". We can't conclude that windy days are particularly dangerous from this data without knowing how often planes fly in windy conditions.

The question also only asks for what causes the most accidents: that lets us skip past relative probability of the underlying condition. The question doesn't ask what condition, when present, is the most likely to cause an accident. The data does not create a base-rate fallacy. It actually answers the question that was asked. But yes, we should not draw any further conclusions from it.


text:
Velocity change after a 15-deg climb in one second
I am trying to make a very simple model to simulate aircraft motion, using velocity only. I don't want to make it complex by using lift, drag, thrust, etc.
When an airplane, flying at 200 m/s at time 0, pitches up 15 deg at time 1 without increasing thrust, is it reasonable to say that its velocity will decrease to 193.2 m/s at time 2 and it climbs to 50 m?
I calculated those numbers using vector sum shown below.
200 * cos(15) = 193.2 (the length of the blue arrow below)

No. Closer to 197 $\frac{m}{s}$.

Can you please show me how you calculated 197 m/s?

By assuming conservation of energy one can equate $m g \Delta h = 1/2 m (v_1^2-v_2^2)$. With this you see that the answer should be 197 $\frac{m}{s}$. While I think it is an interesting idea to simplify flight dynamics calculation, I do not think that triangles are physically correct... However perhaps it is enough for your needs? Though it might be arbitrarily incorrect...

@U_flow Energy conservation is not the right thing to use here. The thrust is unchanged, not turned off. Even if it were turned off, energy conservation would still be wrong since it doesn't account for drag.

Basically by using energy conservation, you're simulating a projectile. That's not an aircraft by any stretch of the imagination!

If an airplane flying at 200m/s suddenly pitches up of 15° it either stalls or get destroyed... You cannot use only velocity to describe the flight physics of an aircraft... unless your aircraft is a spherical cow in vacuum

@Chris Energy conservation is the right tool to use here because the thrust is not turned off! As the aircraft is in level flight before the pitch up, we know that Thrust = Drag. After the pitch up maneuver, momentarily we can assume that still T=D however with the addition of the gravity component. I agree that after some time the aircraft will settle to its new equilibrium, but not in one second. For this reason, energy conservation can be used as an approximation as all other forces stay roughly the same on this time-scale.

In the real world, if one were to instantaneously command a flight path angle (gamma) of 15 deg from level flight, there would be a significant angle-of-attack transient. Therefore, for the sake of this thought-experiment question, if you assume angle-of-attack is very small throughout and somehow gamma makes an unphysical step change from 0 to 15 deg, then thrust and drag haven’t changed in that instant so still cancel each other out. Then, the deceleration rate is equal to simply g*sin(gamma) or approximately 2.54 m/s/s.
Of course, as the velocity decreases over time, drag will be less and thrust will change slightly with velocity and altitude. However, over only one second, the assumption of thrust remaining equal and opposite to drag is reasonable. 200 - 2.54 = 197.46

No. The speed will change to whatever balances thrust, lift, drag, and weight. There's no way around it.
The simplest model you can make that has any degree of accuracy is to treat weight as a constant, lift and drag as functions only of velocity, and thrust as a variable. This approximates the hands-off flight of an airplane at a specific trim setting (so that it always flies the same angle of attack).
Such a plane can't do the maneuver you ask about in your question though- it is unable to pitch up at constant thrust. That requires pitch control, and with it you have to model how lift (and drag, if you like) vary with angle of attack.


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What is the weight of the bulletproof cockpit doors of a Boeing 747?
What is the weight of the bulletproof cockpit doors of a Boeing 747 built prior to 9/11? Do the doors weigh the same for later models, like the Boeing 747-8 specifically? How many fewer passengers do they have to carry in light of the added weight?

Downvoters, please remember to include an explanation. The OP can't make the question better if they don't know what's wrong

Why did this receive 5 downvotes? It's a perfectly valid, on-topic question.

@DeltaLima People seem to be downvoting the user and not the questions. After the meta post, people seem to be following the rule of "if you can't say anything nice, don't say anything at all."

@foot, thank you for your response. If you are right that the user is downvoted instead of the question, I wonder on what basis that is done. In my opinion, voting should be based on the content of the post. I understand that voting is sometimes biased based on historic behaviour of a user, because post are judged in that historic context. The bottom line is that this is a perfectly valid, clearly phrased, aviation related question. Down voting such a question doesn't help this site, nor the person who asked the question.

People downvoted this as SO can be a pretty arrogant community. No AI has taken over it so you won't get woke devs and woke arrogant replies


text:
What is the sweep angle of the Boeing 787's horizontal stabilizers?
What is the sweep angle of the horizontal stabilizers on a Boeing 787 Dreamliner? Does it have to be equal to that of the wings, and how is it determined?

I'd say about the same as the main wings, but I've no protractor at hand.


text:
What happens to the control systems of a BAe 146 when the aircraft runs out of fuel?
On a BAe 146, is there any way to control the aircraft when it's out of fuel? Does the APU run on a separate tank? Can the engines be windmilled for power generation?

related: Do jet aircraft have an emergency propeller?

Related: If a typical passenger plane had total failure of all engines mid-flight, is it possible for passengers to survive?

is there any way to control the aircraft when it's out of fuel?

Yes

Does the APU run on a separate tank?

No.

Can the engines be windmilled for power generation?

Yes.

Control
Pitch and roll can be controlled mechanically.
The rudder needs hydraulic power - which can be provided from the emergency DC battery via a pump if the systems are configured appropriately for this by the pilots.
There is a magnetic compass and a minimal set of other instruments powered by the emergency DC bus.
Fuel / Generators
The four engines, including the two with generators, each have a separate feed tank that is fed from the main tanks.
When fuel stops reaching the feed tanks, warnings are shown/sounded in the cockpit. I vaguely recollect the feed tanks may have something like 20 mins fuel (could be less).
The APU is fed from the same main fuel tanks as the main engines.
Electrics
The electrical system has three modes

normal
essential
emergency

I believe that there is 30 minutes electrical power available from the emergency battery that powers the EMERG DC bus. There is an inverter that takes power from EMERG DC and provides power to the EMERG AC bus.
RAT
An overview schematic (allegedly for 146) does not show an emergency ram-air-turbine (RAT) generator.

Hydraulics
There are two Hydraulic systems, yellow and green. Each powered by a separate engine.
There is a DC pump that provides hydraulic power to the yellow system from EMERG DC power. There is a switch in the cockpit to control this.
Windmilling
A limited amount of hydraulic power can be generated by windmilling the engines but the pilots have to reduce the load on the engines by deselecting the standby generator.
One of the windmilling engines will be driving the emergency fuel pumps (obviously uselessly if you actually run out of fuel mid-air, rather than having problems with main pumps)

References

QualityWings flight simulation manual :-(
satcom.com


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Why do jet planes with multiple engines have separate throttle levers for each engine?
What are the reasons to not just use one throttle lever for all engines?

All multi-engine airplanes, whether jet or prop driven have separate throttle controls for each engine. There are good reasons for this:

If there is a problem with one engine you can separately control it for troubleshooting purposes
If one engine isn't developing the right amount of power you can independently increase the other engine(s) to compensate
If you have a control failure of some kind you can use differential thrust to steer the airplane, this has been done more than once, the example that comes immediately to mind is United 232

Most modern engines use digital electronic FADEC control. It would be very easy to have one thrust lever and still accommodate separate control for all the reasons given above. I have to assume the really reason might be something else. ( like tradition)

Differential thrust is also very helpful in taxi, not just in the event of control failure. I often use differential thrust as my primary directional control in taxi.

@Mike Sowsun: Turn the question around, though, and ask whether there are any good reasons to have a single throttle control.  I can't think of any, but then I'm used to just having one engine :-)

To extend the question considering this answer and comments: are there devices that can selectively 'gang' all thrust levers, to avoid unintended differential settings? Like when a pilot wants to move all to TOGA but lets one slip?

There are military twin-engine jets with a single 'throttle'. Rafale, for example.

@RobVermeulen, the levers are always made such that you can grab them all at once and move them together. In many aircraft the significant settings (TO/GA, MCT, FLEX, CLB and IDLE) also have detents to assist in precise positioning of the levers.


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What are the drawbacks for manufacturing a large airliner capable of water landing?
Emergencies are rare but still occur. Apart from weight and extra fuel costs, What are the drawbacks for manufacturing a large airliner capable of water landing in case of an emergency?
Assuming the extra weight problem could be mitigated through design and cost cutting techniques and advances in material science would this be feasible for airliners?

How soon we forget :-)  Modern airliners are capable of water landings in an emergency: https://en.wikipedia.org/wiki/US_Airways_Flight_1549

There were times when large airliners could only land on water :) But it didn't last...

@securitydude5 this question is a little vague in some ways. Drawbacks in cost? Consumer appeal? Aerodynamic compromises? I'd rewrite the question to get a specific answer that you're looking for.

"Apart from weight and extra fuel costs" is quite the caveat, since fuel is a major part of an airline's costs. The mitigation doesn't quite make sense, either, unless you assume that the material science gains wouldn't apply to non-water-related materials. If they apply to all materials, then adding the water-related components would still increase weight relative to that new state of the art.

Maintenance. Ditching survivability calls for overwing engines, as underwing ones act as scoops and torque the aircraft. But underwing engines are quieter for the pax and much easier to access. Plus, you'll need to make most of the openings airtight, and regularly inspect and replace the seals.
But of course weight, drag and extra fuel are a big deal - with better materials you'll still be picking between better reducing fuel usage or improving ditching survivability. The latter is also only helpful in controlled ditchings, which are mostly being prevented through engine reliability.
That said, airliner design has shifted from "don't crash" to considering crashworthiness at every stage. So it's possible that ditch-worthiness might become a larger factor in design. But it's going to take a couple high-profile high-fatality controlled ditchings for the authorities to make the call to sacrifice fuel efficiency for it, which is currently a big deal due to rising oil costs and AGW concerns.

If we're talking safety, underwing engines have the large advantage of being able to shear off without taking the wing out. That's intentional. Landing with one engine is much easier than landing with one wing.

Yeah. But a landing without losing either is even better. Scooping engines do enough harm before shearing off to make a smooth landing much less likely.

I wasn't considering the rare ditching, but engine problems in normal flight. In that case, it's fairly safe if one engine drops off entirely, without damaging the wing. That's the reason why underwing engines are preferred.  Putting engines over the wing may make ditching safer but makes other engine problems less safe.

Airliners are already designed to survivably land on water in an emergency. You usually can't reuse the aircraft after you do, but it is a certification requirement. See 14 CFR 25.801

(b) Each practicable design measure, compatible with the general characteristics of the airplane, must be taken to minimize the probability that in an emergency landing on water, the behavior of the airplane would cause immediate injury to the occupants or would make it impossible for them to escape.

If aircraft were not designed to reasonably land on water, then they wouldn't bother putting in rafts and the lifejackets under your seat.

If you are talking about seaplanes, or designing an amphibious airliner, this biggest drawback would be excess drag from such a configuration, a less than optimal aircraft configuration to accommodate seaplane characteristics, adding to weight, increased costs due to maintenance, passenger discomfort from landing on rough seas.  The last major examples of large flying boats for passenger or cargo use were the Martin S2B SeaMaster and the Hughes H-4 Hercules (better known as the Spruce Goose). Both aircraft never progressed passed the flight test stage due to the global proliferation of terrestrial runways in the PostWar era and no military usefulness once the German U-Boat threat disappeared from the Atlantic.  And there’s really no valid reason to design an airplane that way in the era of highly reliable engines and multiple system redundancy.

There are in fact valid reasons to design a fairly large airplane this way, such as firefighting, access to remote areas, &c.  Granted that it's a niche market, but there are such planes in (recent) service, e.g. https://en.wikipedia.org/wiki/Beriev_Be-200

But there is no market for a large airliner like that.  Those roles are already well filled by existing, smaller seaplanes and amphibians.  It would be difficult if not impossible these days to design a large flying boat along the lines of the Spruce Goose and have it be commercially successful.

You say there is no market, but Beriev builds and apparently sells one.

The Beriev aircraft is relatively small compared with the Spruce Goose and Beriev doesn’t sell very many aircraft.  It’s not a lucrative business model for the likes of Boeing or Airbus.

Re "relatively small compared with the Spruce Goose", what isn't?  As I said, it's a niche market, but nevertheless, it is a market.

If you’re going to manufacture a large airliner, there is no point in making a flying boat with today’s modern engines, systems and available terrestrial airports.  Design teams would look at a proposal for such an aircraft and ask “why would I do that?” when faced with all the drawbacks of such a design to make the extremely remote chance of a forced water landing easier (maybe, depending on how rough the seas are).  No airline would buy the thing.


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What type of engine is mounted on the Cessna Citation Hemisphere?
What type of engine is mounted on the Cessna Citation Hemisphere?
Image Source

That does not look like a high bypass turbo jet engine.  If its not a high by pass turbo jet engine, and given a high bypass turbo jet engine is the most efficient engine, why was it not used for this particular aircraft and why was the particular engine chosen for this aircraft given its cruise speed is similar to that of aircraft that use the high bypass tubo jet engine?

The Cessna website mentions the engine type used (emphasis mine):

The Citation Hemisphere will be powered by two next-generation Safran™ Silvercrest™ engines delivering over 12,000 pounds of thrust. The Silvercrest engines incorporate the latest advanced, field-proven technologies to offer unrivaled performance in its class in terms of direct operating cost, propulsion efficiency, reliability and environmental friendliness. These engines lower fuel consumption by up to 15 percent, reduce NOx emissions by up to 40 percent under CAEP/6 standards and half the noise footprint compared to other engines in its class.

According to Wikipedia, this engine will have a bypass ratio of
$$5.9 \, : \, 1 $$
which would certainly count as a high-bypass turbofan engine. Also see: What is the difference between a high bypass turbofan and a low bypass turbofan?

seems the bypass air and hot air have a singe exit at the back hence the question

@securitydude5 This question should answer that.

It's more of a not-so-high bypass turbofan compared to turbfans used in airliners.  Bypassing air trades low mass/high velocity for more mass/lower velocity (take that to the extreme and you have a turboprop) and at high altitudes where there isn't much mass to work with, it's better to go with a bit less bypass in corporate aircraft that cruise about 10000 ft higher than airliners.


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What are the pros and cons of using shielding as opposed to liquid cooling the skin of supersonic aircraft?
What are the pros and cons of using shielding as opposed to liquid cooling the skin of supersonic aircraft? This is in light of the fact that most shielding materials used in aircraft, like ceramics, are very heavy. Could a radiator with 100 liters of water possibly weigh less?

Shielding is cooling, but air cooling. Where there is plenty of air flow, it's hard to beat air cooling. Liquid cooling only has the advantage when there's little air flow, like around the engine it's common to use fuel as cooling medium.

The problem with a radiator is that you need someplace to dump the heat.  With a car, you can put a radiator out front in the cool(er) air flow, but it still causes drag.  At supersonic speeds, that radiator would be heated even more than the skin of the plane, not to mention that the drag would make it highly inefficient at best.

I’m not aware of any supersonic aircraft which use ‘shielding’ to protect them from atmospheric friction heating, save for rockets, and a few experimental platforms like the X-15B which used an ablative coating, mostly of cork or rubber, which slowly burnt off during the flight, protecting the aircraft structure underneath.
As for cooling systems, I suspect that the weight of a network of tubes throughout the skin of the aircraft coupled with a heat exchanger and pump to circulate cooling fluid through them was too expensive and complex.  A more efficient method is simply to use the aircraft’s fuel as a heat sink and absorb atmospheric friction heat be slowly warming the fuel in the tanks.  It’s a lighter and simpler solution.
Ceramic protective layers, such as the tiles on the exterior of the space shuttle orbiter can be made fairly light when they are a matrix of nitrogen gas pockets inside of them.  They are quite effective a heat protection on a unit mass basis but can be difficult and expensive to maintain.
Since the 1970s there have been few aircraft programs venturing past Mach 2 so practical applications of heat protection for airframes has been limited.  We will have to see what new developments in military hypersonic vehicles, such as Lockheed’s SR-72 reconnaissance aircraft, are using to address atmospheric heating.

Shielding isn't used on aircraft. Only on spacecraft like the Space Shuttle do you get surface elements whose only function is a heat shield.
The problem with a radiator is that the whole aircraft is being heated, so your radiator has only a slight temperature gradient to work with. That means it needs to be very large (i.e. heavy).


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Could adding a gearbox to the Trent 900 improve the efficiency of the A380?
Could adding a gearbox to the Trent 900 improve the efficiency of the A380 so that it performs better than a smaller jet, i.e with economies of scale? Is the absence of a gearbox in the Trent 900 the main impediment to the efficiency of the A380?

If I had to guess, it would be that the engineers at RR are really pretty good and would have added a gear box if it had a good cost/benefit effect.

It would not be a simple task to add a gearbox to an existing engine like the Trent 900. The whole engine is designed to operate as a whole, with each of the three shafts rotating at an optimal RPM. The gearbox would have to be designed to work with the existing engine hardware, which would mean compromises on efficiency. The engine would also have to be modified to find room to fit the gearbox in.
A gearbox also does not automatically mean an engine will be more efficient. The geared PW1000G achieves similar efficiency to the CFM LEAP which does not have a gearbox.
It's much more likely that a new engine would be designed for the A380. Airbus has previously said that this was planned for some point in the future. However, a new engine is not cheap for either the engine company to develop or for Airbus to integrate. The A330 and A320 programs have gone this route but they are also designs with high demand.
A new engine would have to generate enough demand to justify the cost, and it does not seem that Airbus sees this demand yet. Airbus has been struggling to find new orders for the A380 and has been slowing down production. It's not clear that better efficiency is enough to make the plane sell. Four engine planes are inherently limited in their efficiency versus twin engine planes. The four engines add more drag and weight versus two engines, and increase maintenance costs.
The A380 also requires special accommodation in the air and on the ground for its large size. The 747 has been around for much longer and does not need as many special accommodations. Boeing went to the expense of redesigning the wing and adding new engines for improved efficiency, yet is still struggling to find orders.
More recently Airbus has announced that they are considering "A380 plus" which will include new winglets, wing changes, and other design tweaks to improve efficiency. This will be a much cheaper way to add efficiency than a new engine, if that efficiency will mean more orders.


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Would propellers be more efficient if they were mounted at the rear of the aircraft?
The propellers of a front-mounted propeller plane push air back directly on a collision course with the aircraft's body. That results in zero thrust or negative thrust from at least some sections of the propeller that are close to the body, thus making the engine work harder and use more fuel as the air bounces back from the body towards the propeller.
Would it not be better to mount single propeller engines somewhere at the back of the plane, where all of the propeller is generating thrust?

I believe you're asking if pusher propellers are more efficient than pullers

Your question was very difficult to understand, I've simplified it to what I think is the core point you're getting at, but if I got it wrong then you can just re-edit or roll back.


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What is the maximum weight on the main gear of a large aircraft at rotation and touchdown?
For a large aircraft like a B747 or A380, how much does the weight on the main gear increase when the nose gear is in the air? I mean, in these two cases:

What is the maximum extra weight on the main wheels when rotating at maximum takeoff weight, with the nose wheel off the ground?
What is the maximum extra weight on the main wheels when touching down at maximum landing weight, with the nose wheel off the ground?

For (1), the weight will be less than the total weight of the aircraft since the wings are generating lift and helping hold some (most) of the weight up. As for (2), at the exact moment of touchdown it is some function of the speed of touchdown and the weight of the aircraft, along with how much lift is being generated.

Related: How much force does a 747 land with?

There's more weight on the main gear when the aircraft pushes back from the ramp and is taxiing than on the takeoff roll, due to the lift generated from the wings. When the aircraft rotates the higher angle of attack generates enough lift to 'offset' the aircrafts weight and it takes off.
The most weight a main gear set will take will be on a firm landing at max landing weights (or above in an emergency). On the 737 there is a 'hard landing' G limit of (i think) just over 2G. So in theory temporarily on touchdown the main gear between them are handling twice the aircrafts weight.
As an example for the 737:
MTOW 77 tons.
MLW 65 tons.
4 main gear wheels.
heavy take off = 77/4 tons when parked ready to push back, reducing to 0 on rotation.
ie roughly 20 tons per wheel and tyre.
adding in landing G forces...
firm landing (but in limits) = (65*2)/4 tons on touchdown, quickly reducing back to 65/4.
ie roughly 32 tons per wheel down to 16 when parked up.
emergency landing after take off at MTOW = (77*2)/4 tons at touchdown. 36 tons per wheel!


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Would it be possible to build an engine twice the size of the Trent 900?
Would it be possible to build an engine twice the size of the Trent 900 in terms of physical size, i.e. doubling the diameter?
Let's assume that it's feasible to build an aircraft tall enough to install the engines. I will go on to ask about the extra heat at the engine core or hot sections of the engines but to run such an engine, would current materials be able to tolerate the extra heat? Would the larger fans tolerate the extra stresses if the diameter doubled?

Won’t be able to answer this myself, but do you mean twice the physical size (in terms of fan diameter etc.), twice the volume/weight, or twice the thrust? I assume that will make quite a difference in feasability.

Sure, just open up the drawing files, scale by a factor of 2, and then send it off to production.

@RonBeyer it'll only be 8 times heavier, what could possibly go wrong?

@fooot Plus they would have to put the aircraft on stilts to get the engine under the wing

"As incomes rise, I think jumbos like the A380 would sell tickets at a premium..." The A380 has problems selling tickets at all, much less "at a premium". If Emirates doesn't order more aircraft, Airbus will most likely halt the A380 production only 10 years after its introduction. The 747-800 is having similar problems as it isn't being flown in passenger service by many operators anymore.

People that buy luxury goods are not price sensitive

@securitydude5 Even if they aren't, Airbus/Boeing is, and isn't going to maintain production of the jet for 1 or 2 customers/aircraft.

1 or 2 customers of Airbus or Boeing are not the entire Luxury Air travel market.  Even if they were, the market is much bigger than they are currently serving & so if those customers can make super profits with those jets serving the entire market &demanding more because the market is larger, then it would make sense to continue making the air craft. Afterall there were development costs in the beginning. In any case the jets could not achieve economies of scale because thy have to compete with fuel efficient geared turbo fans. continued...

...continued Who knows latest developments converting Co2 in the artmosphere, at a much lesser cost could make fuel a lot more cheaper

"it would make sense to continue making the aircraft"... What makes sense is to sell the aircraft. That's what covers the salaries. Airbus had plans for extended versions of the A380, they will probably never been built.

If Airbus is selling the A380 profitably and those that buy the A380 are able to use it profitably as anticipated or even better, they will be able to pay salaries and continue to demand the Airbus A380 and it will make sense for Airbus to continue making the aircraft.  Remember its the business class and 1st class passengers that subsidize the seats of he economy class and make air travel affordable for them despite their numbers. Creativity on the side of those buying the A380 for use i.e more luxury and prestige premium service, will keep the aircraft in manufature

"If Airbus is selling the A380 profitably and those that buy the A380 are able to use it profitably as anticipated". Indeed this is the idea behind aircraft marketing, and for that matter behind any B2B product, but we know this is not the case due to the anticipated hub deployment in airlines which has not materialized since the plane was designed. Wealthy people are likely those less interested in the hub (mass) mode, they want customized services.


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Is it possible for an Airbus A380 to operate with 8 of the largest geared turbofans instead of 4 Trent 900 engines?
Is it possible for an Airbus A380 to operate with eight of the largest geared turbofans instead of four Trent 900 engines? Would it be fuel efficient? What would be the total thrust of the engines?

Why 8, why not 6. Random question. "What would be the total thrust of the engines?", well if you know which engine is the largest GTF, then don't you have already the answer? "Would it be fuel efficient?": After redesigning the wings, maybe. What do you mean by "fuel efficient", a phrase you use a lot in your A380 questions?

This is a subset of your other question. I’m relatively sure that rated thrust of „the largest GTF“ should be a googleable number, is it not?

The current largest geared turbofan is the PW1100G. The highest thrust variant is the PW1130G which provides 147.28kN of thrust. Eight of these would provide 1178kN total thrust.
The Trent 900 provides 340kN of thrust, the 4 engines on the A380 provide a total of 1360kN of thrust. This means that 8 PW1130G engines would leave the A380 a bit under-powered.
Would it be efficient? Probably. Most of the efficiency of an airplane comes from the engines. The PW1100G are newer and more efficient than the Trent 900 engines. There would be some losses due to higher installation drag but probably not enough to offset the efficiency.

Pro efficiency: Newer engines; optimised design; more of them means less total thrust required to cover engine failure (provided certification allows credit). Against efficiency: More installation drag per engine; less efficient wing (there’s no undisturbed part of wing anymore - engines everywhere); less efficient high pressure sections (ratio of blade gaps/engine diameter larger). Effect unclear: weight changes due pylon/wing structure & more complicated fuel system with smaller diameter pipes etc.

+1. Just wondering if there would be a customer for an A380 with 8 engines to maintain. Maybe because it would have the ETOPS 600.

I’m definitely not claiming my list to be comprehensive in any way, I should add.

@mins there are barely any customers for an A380 with 4 engines to maintain. :P